Thixotropic metal-containing monomethylhydrazine fuel and method of preparing the same

ABSTRACT

A composition consisting of gelled monomethylhydrazine containing dispersed therein up to 70 weight per cent finely divided metallic fuel particles that are compatible with said monomethylhydrazine and a cellulose or hydroxyalkyl-substituted cellulose gelling agent.

United States Patent 1191 Allan Dec. 31, 1974 THIXOTROPICMETAL-CONTAINING [56] References Cited MONOMETHYLHYDRAZINE FUEL ANDUNITED STATES PATENTS METHOD OF PREPARING THE SAME 3,164,505 l/l965Hsieh et al 149/36 [75] Inventor: Barry D. Allan, Huntsville, Ala.FOREIGN PATENTS 0R APPLICATIONS [73] Assignee: The United States ofAmerica as 978,105 12/1964 Great Britain 149/36 represented by theSecretary of the Army, Washington, DC. Primary Examiner-Leland A.Sebastian I Attorney, Agent, or FirmEdward J. Kelly; Herbert [22] Flled1966 Berl; James T. Deaton [21] App]. No.: 518,489

EXEMPLARY CLAIM 521 U.S. Cl 149/20 149/197 149/21 A misting gelledmOmmethYlhYdra' 149/22 149/36 149/118 zine containing dispersed thereinup to 70 weight per 51 Im. c1 C06b 19/04, (5061: 1/02 Cent finelydivided metallic fuel Particles and 3 5 Field of Search 149/3 1 2O, 4 91111086 OI hydroxyalkyl-substituted cellulose gelling 149/21, 22, 11sagent- 6 Claims, 3 Drawing Figures PATENTEDBHBIBH sum 2 OF 3 50/o AL PISFIG. 2

Barry D. Allan,

INVENTOR.

p. CENTIPOISE PAIENTEDBEB31 W 3'. 857. 743 SHEET 3 OF 3 SPEED RPM(BROOKFIELD) FIG. 3

Barry D.Al|c|n,

INVENTOR.

BY M J, /W W M THIXOTROPIC METAL-CONTAINING MONOMETHYLHYDRAZINE FUEL ANDMETHOD OF PREPARING THE SAME The invention described herein may bemanufac tured and used by or for the Government for governmentalpurposes without the payment of any royalty thereon.

This invention relates to rocket fuels and more particularly to gelledmonomethylhydrazine containing metallic particles.

Monomethylhydrazine, commonly referred to as MMH, is useful as a liquidfuel for rocket motors. This material exhibits favorable combustionproperties when reacted with an oxidizer such as nitric acid, a specificimpulse, Is, of 278 seconds (l,000-. l4 psia) being obtained. Forapplications where fuel-tank volume is limited, it is desired toincrease the density of MMH while maintaining a high specific impulse.The effectiveness of the fuel in this regard is expressed in terms ofspecific impulse-density, p Is, the product of density and specificimpulse values. The specific impulse-density value for MMH nitric acidis 355.8.

One means of increasing the specific impulse-density of MMH fuel is toprovide finely divided particles of a metal such as aluminum in the MMH,this measure having been employed previously for solid propellants. Suchan approach has not been practical for liquids such as MMH, however,owing to the difficulty of maintaining the particles in suspension. Thefuel is normally stored in a tank on board the rocket for an extendedperiod prior to firing, and the metal particles settle to the bottom ofthe liquid. The resulting inhomogeneity could not be tolerated inoperation of the rocket motor. Stability of the metal-containing fuel isalso adversely effected by vibration and acceleration forces encounteredin flight of the rocket.

in order to maintain the metal particles in suspension and yet allowpumping of the fuel as a liquid the metalcontaining MMH should beprovided in the form of a thixotropic gel, which behaves as a stablesolid until disturbed, but flows as a liquid when force is applied.

Provision of metal-containing MMH in the form of a thixotropic gel wouldalso reduce the hazards associated with MMH. This material is highlytoxic, and when handled in liquid form, extreme precautions must betaken to avoid leakage or escape of fumes. Furthermore, MMH reactshypergolically with many common materials so that a leak could cause adisastrous fire. The reduced mobility of a gel as compared to liquid MMHwould avoid these dangers.

It is therefore an object of this invention to provide a stablesuspension of matallic fuel particles in MMH.

Another object is to provide a method of converting metal-containing MMHto a thixotropic gel.

Still another object is to provide a MMl-l rocket fuel having increasedspecific impulse-density.

Other objects and advantages will be apparent from the followingdetailed description.

In accordance with the present invention a thixotropic MMH gelcontaining metallic fuel particles is prepared by dispersing the fuelparticles and a cellulose or hydroxyalkyl-substituted cellulose gellingagent in the MMH. The gelled, metal-containing MMl-l exhibitssubstantially increased specific impulse-density values, and the metalparticles remain in suspension indefinitely. The gel can be pumped andfed into a rocket motor combustion chamber as a liquid by application ofmoderate stress. The semi-solid character of this fuel minimizes thetoxicity and fire hazards associated with handling and storage of liquidMMH.

Any cellulose or hydroxyalkyl-substituted gelling agent may be employed,and the following commercially available gelling agents, listed by theirchemical composition and trade mark designation, are preferred: hydroxylmethyl cellulose containing 27.5 to 3.15 weight percent methoxyl groups,Methocel; hydroxypropyl methyl cellulose containing 28 to 30 weightpercent methoxyl groups and 7 to 12 weight percent propoxyl groups.Methocel HG-60; hydroxypropyl methyl cellulose containing 19 to 24weight percent methoxyl groups and 4 to 12 weight percent propoxylgroups, Methocel HG-90; dihydroxyethyl cellulose, Cellosize; andhydroxypropyl cellulose containing about 4.6 propoxyl groups per glucoseunit, Klucel.

The gelling agent is provided in an amount sufficient to inpartthixotropic character to the metal-containing MMH, a room-temperatureviscosity of at least about 15,000 centipoise being required, and 30,000to 60,000 centipoise being preferred. For the preferred gelling agentsgiven above, 1 to 3 weight percent gelling agent in the mixture issuitable for this purpose. The viscosity can be controlled by varyingthe amount of gelling agent, higher viscosities being obtained by largeramounts. The amount of gelling agent required to obtain a givenviscosity varies somewhat with the physical properties of the metallicparticles, smaller amounts being required for particles having a largersurface area.

The term metallic fuel particles as used herein is intended to refer toany of the finely divided metals and metal hydrides previously used asfuel in solid propellants. Aluminum, magnesium, boron, beryllium, leadand zirconium and hydrides thereof can be used. The metallic particlesmust be finely divided in order to remain in suspension and allowpumping of the gel as a liquid, and very fine, generally sphericalparticles on the order of 6 to 10 microns in diameter are preferred.Platelet-type particles, for example, rectangular shapes 40 by 25 by 0.7to 0.8 microns in size may also be used. The composition of themetal-containing MMH gel can be varied within wide limits to obtain theperformance characteristics desired for a given application. The amountof added metallic particles is selected, depending on the desiredtrajectory and mission for the particular missile. Up to about weightpercent metalic particles can be incorporated in the gel and still allowadequate mixing and pumping as a liquid over a practical range ofoperating temperatures. For typical applications 20 to 50 weight percentprovides maximum overall advantage. The particular metal or hydride islikewise selected, depending on the properties desired. Aluminum andboron are desirable because of their favorable combustion properties andtheir ready availability in powder form. Beryllium and beryllium hydrideprovide maximum performance characteristics, but the toxicity ofberyllium combustion products limit their usefulness. Lead is preferredfor applications requiring maximum density.

The metal-containing MMH gel can be prepared by mixing the metallicparticles and the gelling agent with the MMH in a conventional mixer.The gelling agents mentioned above are normally available as finelydivided powder which disperses readily in the MMH. The mixing timerequired for complete dispersion varies with the particular apparatusand the amount of metallic particles, with longer times being requiredfor larger amounts. Under typical conditions a mixing period of one-halfto 2 hours is suitable.

The invention is illustrated by the accompanying drawings wherein:

FIG. 1 is a graph showing calculated specific impulse values for MMHcontaining varying amounts of aluminum at varying oxidizer-to-fuelratios, the oxidizer being inhibited red fuming nitric acid.

FIG. 2 is a graph showing calculated specific impulsedensity values forthe same compositions; any

FIG. 3 is a graph showing the effect of added gelling agent or theviscosity of aluminum-containing MMH.

Referring to FIG. 1, it is seen that specific impulse values aredecreased with increasing amounts of aluminum, except at the lowestoxidizer-to-fuel ratios.

FIG. 2 shows that specific impulse-density values are substantiallyincreased with increasing amounts of aluminum. For example, at anoxidizer-to-fuel ratio of 2, the specific impulse-density valueincreases from less than 370 at weight percent aluminum content to over400 at 50 weight percent.

FIG. 3 depicts the results obtained by adding varying amounts ofhydroxypropyl-substituted cellulose containing 4.6 propoxyl groups perglucose unit (Klucel) to MMH containing 35 weight percent aluminum inthe form of spherical particles averaging 6 microns in diameter. CurvesA and B show the viscosities in centipoises at varying spindle speeds instandard Brookfield viscosity tests for a 125 milliter portion of themetalcontaining MMH with 1.6 and 2.2 weight percent respectively, ofgelling agent. In each case the MMI-I, aluminum and gelling agent wereplaced in a mixing chamher, and the resulting mixture was agitated for aperiod of about 1 hour. It is apparent from the curves that a viscosityover 15,000 centipoise, as is required to maintain the particles insuspension, can be obtained by ad dition ofa small amount of gellingagent. The resulting gels were left standing for a period of over 8months and no settling of particles of other deterioration was observed.

The compositions given in the drawings are merely illustrative and arenot to be understood as limiting the scope of the invention, which islimited only as indicated by the appended claims. It is also to beunderstood that various changes and modifications in apparatus andprocedure may be employed by one skilled in the art without departingfrom the scope of the invention.

What is claimed is:

1. A composition consisting ofgelled monomethylhydrazine containingdispersed therein up to weight percent finely divided metallic fuelparticles and a cellulose or hydroxyalkyl-substituted cellulose gellingagent.

2. The composition of claim I wherein said gelling agent is methylcellulose containing 27.5 to 31.5 weight percent methoxyl groups,hydroxypropyl methyl cellulose containing 28 to 30 weight percentmethoxyl groups and 7 to 12 weight percent propoxyl groups,hydroxypropyl methyl cellulose containing 19 to 24 weight percentmethoxyl groups and 4 to 12 weight percent propoxyl groups,dihydroxyethyl cellulose or hydroxypropyl cellulose containing about 4.6propoxyl groups per glucose unit.

3. The composition of claim 2 wherein the amount of said gelling agentis l to 3 weight percent.

4. The composition of claim 3 wherein said metallic fuel particlesconsist of aluminum, magnesium, boron, beryllium, lead, zirconium,aluminum hydride, magnesium hydride, boron hydride, beryllium hydride,lead hydride, or zirconium hydride.

5. The composition of claim 4 wherein the amount of said particles is 20to 50 weight percent.

6. The method of preparing a thixotropic monomethylhydrazine gelcontaining finely divided metallic fuel particles selected from thegroup consisting of aluminum, magnesium, boron, beryllium, lead,zirconium, aluminum hydride, magnesium hydride, boron hydride, berylliumhydride, lead hydride and zirconium hydride which comprises mixing saidparticles and said monomethylhydrazine with l to 3 weight percent ofmethyl cellulose containing 27.5 to 3 l .5 weight percent methoxylgroups, hydroxypropyl methyl cellulose containing 28 to 30 weightpercent methoxyl groups and 7 to 12 weight percent propoxyl groups,hydroxypropyl methyl cellulose containing 19 to 24 weight percentmethoxyl groups and 4 to 12 weight percent propoxyl groups,dihydroxyethyl cellulose or hydroxypropyl cellulose containing about 4.6propoxyl groups per glu-

1. A COMPOSITION CONSISTING OF GELLED MONOMETHYLHYDRAZINE CONTAININGDISPERSED THEREIN UP TO 70 WEIGHT PERCENT FINELY DIVIDED METALLIC FUELPARTICLES AND A CELLULOSE OR HYDROXYALKYLSUBSTITUTED CELLULOSE GELLINGAGENT.
 2. The composition of claim 1 wherein said gelling agent ismethyl cellulose containing 27.5 to 31.5 weight percent methoxyl groups,hydroxypropyl methyl cellulose containing 28 to 30 weight percentmethoxyl groups and 7 to 12 weight percent propoxyl groups,hydroxypropyl methyl cellulose containing 19 to 24 weight percentmethoxyl groups and 4 to 12 weight percent propoxyl groups,dihydroxyethyl cellulose or hydroxypropyl cellulose containing about 4.6propoxyl groups per glucose unit.
 3. The composition of claim 2 whereinthe amount of said gelling agent is 1 to 3 weight percent.
 4. Thecomposition of claim 3 wherein said metallic fuel particles consist ofaluminum, magnesium, boron, beryllium, lead, zirconium, aluminumhydride, magnesium hydride, boron hydride, beryllium hydride, leadhydride, or zirconium hydride.
 5. The composition of claim 4 wherein theamount of said particles is 20 to 50 weight percent.
 6. The method ofpreparing a thixotropic monomethylhydrazine gel containing finelydivided metallic fuel particles selected from the group consisting ofaluminum, magnesium, boron, beryllium, lead, zircOnium, aluminumhydride, magnesium hydride, boron hydride, beryllium hydride, leadhydride and zirconium hydride which comprises mixing said particles andsaid monomethylhydrazine with 1 to 3 weight percent of methyl cellulosecontaining 27.5 to 31.5 weight percent methoxyl groups, hydroxypropylmethyl cellulose containing 28 to 30 weight percent methoxyl groups and7 to 12 weight percent propoxyl groups, hydroxypropyl methyl cellulosecontaining 19 to 24 weight percent methoxyl groups and 4 to 12 weightpercent propoxyl groups, dihydroxyethyl cellulose or hydroxypropylcellulose containing about 4.6 propoxyl groups per glucose unit.